Loop antenna



Aug. 28, 1945. A. cs. KANDOIAN I 2,333,490

LOOP ANTENNA Filed Obt. 7, 1942 Patented Aug. 28, 1945 LOOP ANTENNA Armig G. Kandoian, New York, N. Y., assignorto Federal Telephone and Radio Corporation. a

corporation of Delaware Application October 7, 1942, Serial No. 461,148 7 This invention relates to antenna. arrangements and more particularly to broad band antenna systems. i

V Antenna systems havebeen proposed in which relatively short radiant'acting elements are arranged in the form of a closed pattern and ener gized opposit diagonal ends of the pattern. Such antenna structures and their operation are more fully set forth in the patent of Andrew Al- 'ford No. 2,283,897 issued May 26, 1942, entitled 'Antenna systems. Inthis type of antenna it has also been proposed to make the radiant acting members relatively massive and in this way it is not necessary to provide a separate capacitive coupling between the units at the ends where the feeding does not take place. I s

For operation at relatively wide frequency bands, it is desirable to support'the radiant acting members in such a way that the supporting members are not subjected to a voltage stress even when the voltage node shifts from the midpoint of the antenna due to a change in the frequency of the energy supplied at the ends of the radiant acting members.

Furthermore, it is often desirable to arrange two or more of these units in a vertical array in order to sharpenthe directivity' in a vertical direction. Whensuch an array is made, it is generally necessary to arrange the feeders for supplying the energy to both sets of units.

It is an object of my invention to provide a loop antenna arrangement operating over a broad. frequency band and supported in such a manner that voltages are not developed across the supporting members with a shift in the wavelength of the exciting voltage. 4 i

It is a furtherobject of my invention to provide a simple feeding system for a vertical array of short wave loopantennae consisting of a plurality of separate radiant. acting members ar ranged in aform of substantially closed'pattern.

In accordance with a feature of my invention the radiant acting members are made of hollow conductive material. The feeding lines are connected to one end of each member and the sup.

porting rods which may be of conductive material are fastened directly to the inner surface of the hollow members and insulated from direct contact with the outer surface thereof.

A better understanding of my invention and the objects and features thereof may be had by reference tothe accompanying drawing; in which:

Fig. 1 is atop plan view partially in section showing the structural arrangement of an antenna inaccordance with my invention;

Fig. 2 is a fragmentary cross-sectional view taken at line 2-2 of Fig. 1; and

Fig; 3 is a perspective :view of an antenna array in accordance with my invention.

,Turning first to Fig. 1, the antenna is composed of four hollow radiant acting members I, 2, 3, 4 arranged in the form of a substantially closed pattern. Substantially centrally of the square is provided a feedline provided with a shield 5 which serves as a supporting mast for the antenna structure. Within the shield 5 are provided two parallel transmission line conductors indicated at 6 and I. These conductors 6 and I are cqnnected by branch lines 8, 9 to the ends of closed members I and 2 and by means of branch lines In and H to the diagonally opposite ends of members 3 and 4. Members I, 2, 3 and 4 all are preferably one half wavelength or less of the operating wave band so'that in effect a current loop occurs in each of the members and the effective currents in each of the members are all in the same direction around the periphery of the closed pattern. Each of the members I, 2, 3 and 4 is preferably made in the form of a semi-cylinder as shown at 20 (Fig. 2) preferably with a metal closure member 2| across the open faceof the cylinder. Likewise, each member is preferably provided with an end closure as shown at l2 (Fig. 1). 1

Such a loop construction has been made with each of the. members about ten inches in length and of a semi-cylindrical form of about-five inches This loop structurewas found to in diameter. operate satisfactorily at frequencies from 300 to 350 megacycles.

However, if the loop is tuned to the mean frequency of this wave band, it is clear-that the voltage node, existing in members I to 4 inclusive, at this tuned frequency, will shift somewhat to either side, thereof, as the frequency is changed toward the ends of the band. Thus, if the support for each member is connecteddirectly to the outside surface thereof, there will be a voltage developed across this support at all the frequencies except the mean frequency.

In order to avoid this effect, I provide supporting members I4, l5, I6, I! fastened at one end to a supporting sleeve I8 directly connected 'to shielded line 5 and at theirother end passing through an opening in the closure member 2| to the inner surface of each of the members where they are securely fastened as indicated at I9. Since each radiant acting member is substantially an electrically shielded circuit, there is substantially no voltage within so that no voltage porting rods for all conditions of operation. The I use of the metallic supports serves as alightning protection for the system. It is'further pointed out that if insulating supports are used a separate conductor fastened to the inner surface of the antenna members and the mast may be provided for lightning protection. t

It is clear, of course, that members I to t, inclusive, may be made in any desired'hollow. form, the semi-cylindrical form being illustrated since it is. a relatively easy form to construct. Likewise, the members may be in other shapes. so that the closed pattern may take other forms, for example, a circle.

In. Fig- 3 is illustrated two of these antenna units mounted on a common supporting shielded conductor line 30. Connections are made .to the opposite diagonal corners of upper unit 3| of the array and from this connection point loads 32 are brought to the corresponding diagonal points of lower unit 33. Preferably, units 3| and-33 are supported about one-half wavelength apart and transpositions 34 are provided in each of lines 32 so that in-phase energization of the two loops may be accomplished. It is. clear, however, that if it is desired that the antenna units be operated in phase opposed relation, the transpositions may be omitted.

Furthermore, if it is desired that the spacing be made. some other value than half a wavelength, the interconnecting lines 32 may be made of proper length to secure the desired phase relationship of energization. I

The antenna array may be connected by means of line 30 to anysuitable translating device such as shown at 35.

It is clear that many modifications in the construction of the apparatus described above may be made within the scope of my invention by those skilled in the art. The particular mounting arrangement for avoiding voltage development across the supporting leadsmayapply to other types of antenna than those specifically shown and described in connection with Figs. 1 and 2.

While I have described the principles of my invention in connection with specific apparatus and particular modifications thereof,,it is to be clearly understood that this description is made only by way of example and not as limitations on the scope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A radio antenna comprising a hollow radiating element, of a given length means for energizing said radiating element, a conductivesupporting mast for said element substantially at right angles thereto, and conductive supporting means substantially at right angles to the lengthwise dimension of said element andsaid mast, fastened to said mast and fastened to the inner surface of said hollow element. I r r 2. A radio antenna comprismga plurality of hollow radiating element's arranged in a substantially closed pattern, each of said elements having a substantially equipotential inner surface means for energizing said radiating elements at their ends, a common conductive supporting mast for said elements extending within said closed pattern, and conductive supporting means for said elements fastened to said mast and fastened to theinner surfaces of said hollow elements.

3. A radio antenna for operating at a wide frequency band comprising a plurality of hollow radiant acting members, each being no longer than substantially one half wavelength at the operating frequencies, said members having substantially equipotential inner surfaces and being arranged in the form of a substantially closed planar pattern, a shielded transmission line substantially normal to said pattern, means for connecting said transmission line to the ends of said members and supporting means for said members fastened at one end to the shield of said transmission line and at their other ends to the inner surface of each of said hollow members. i i r 4. A radio antenna for operating over a wide frequency band comprising four hollow radiant acting members each being no longer than substantially one half wavelength at the operating frequencies, said members having substantially equipotential inner surfaces and being arranged in the form of a substantially closed planar pattern, a shielded transmission line substantially normal to said pattern, means for connecting said transmission line to the diagonally opposed ends of said members and supporting means for each of said members fastened at one end to the shield of said transmission line and at their other ends to the inner surface of the corresponding one of said hollow members.

5. A radio antenna according to claim-4, further comprising a second set of members fastened to the shield of said transmission line in a manner similar to said first set of members, and feeding connections. between the ends of said first set of members connected to said transmission line and the corresponding ends of said membersof said second set. j l

6. A radio antenna according to claim 4 wherein the length of said. members are of the order of between /2 and 1 6. wavelength at the operatin frequencies. Q

7. A radio antenna for operation over a frequency bandcom'prising a hollow radiating element of a given length, means connected to one end of said element for energizing same ata plu-f rality of frequencies-within said band whereby there is a shifting with frequency oflthe voltage node along said element, a conductive supporting mast extending at right angles to said element, and a supporting means extending at right angles to both said element and'said mastconducti-vely connecting said element to said mast, the point of connection ofsaid supporting means to said element being inside said element and such as to have a potential which remains substantially unchanged with variation in frequency.v f

8. A radio antenna for operation over a frequencyfband comprisinga hollow elongated radiating element, means connected to one end of said element for energizing "same, a conductive supporting mast at right angles to said element, and a conductive supporting means connecting said mast to said radiating element at a point having substantially the same potential. as said mast, said supporting'means extending at right angles to both said mast and said element.

' 'ARMIG o. KANDOIAN. 

